The present invention relates generally to fiber optic cables and, more particularly, to fiber optic cables having ultra-low shrinking filaments.
Fiber optic cables include optical fibers that are capable of transmitting voice, video, and data signals. Fiber optic cables have advantages over electrical voice, video and data signal carriers, for example, increased data capacity. As businesses and households demand increased data capacity, fiber optic cables can eventually displace electrical voice, video, and data signal carriers. This demand for fiber optic cables has led to shortages of fiber optic cable materials.
Aramid fibers are cable materials that can serve several functions, such as: providing tensile strength to the fiber optic cable; cushioning the optical fibers from compression and impact loads; covering the optical fibers during the extrusion of the outer jacket to prevent the optical fibers from sticking to the extruded outer jacket; and binding the optical fibers together to prevent relative movement. Aramid fibers can, however, be expensive.
In addition to being cost effective, cables should be simple to manufacture and have a relatively small diameter. An example of a reduced diameter indoor fiber optic cable is disclosed in U.S. Pat. No. 5,627,932, which is incorporated herein by reference. This fiber optic cable requires a tight buffered optical fiber or fibers disposed within a layer of loose aramid fibers, more specifically kevlar(copyright) aramid fibers, which are surrounded by an outer jacket. This cable can be made of flame retardant materials for riser or plenum applications; however, the cable has disadvantages. For example, the cable requires a significant quantity of aramid fibers, which are typically expensive, thereby increasing cable manufacturing costs.
Fiber optic cables should also have acceptable levels of attenuation. An example of a fiber optic cable designed to prevent attenuation as a result of the manufacturing process is disclosed in U.S. Pat. No. 5,822,485, which is incorporated herein by reference. This fiber optic cable or cable element requires a jacket surrounding an optical fiber and aramid fibers, such as kevlar(copyright), without an intended lay. The manufacturing process requires that the tension applied to the aramid fibers during manufacturing does not exceed the tension applied to the optical fiber during manufacturing. Although this fiber optic cable is designed to prevent attenuation induced during the manufacturing process, this design has several disadvantages. For example, the cable requires a significant quantity of aramid fibers, which are typically expensive, thereby increasing cable manufacturing costs.
FIG. 1 (prior art) is a cross-sectional view of a fiber optic premises cable 10. Cable 10 comprises four ends of aramid fibers 12, more particularly four 2450 denier kevlar(copyright) fibers, forming a layer 16 that can be layless or stranded around a single tight buffered optical fiber 14. Outer jacket 18 generally surrounds layer 16. The present inventor has discovered that cable 10 only requires two of the four aramid fibers 12 to provide the requisite tensile strength, the two additional aramid fibers 12 are required to provide coverage and padding for optical fiber 14.
An aspect of the present invention includes a fiber optic cable having at least one optical fiber component, at least one strength member and at least one ultra-low shrinking filament. The at least one ultra-low shrinking filament having a shrinkage of about 0.2% or less when heated and held at about 85xc2x0 C. for about seven days. The at least one strength member and at least one ultra-low shrinking filament being disposed generally between the at least one optical fiber component and a jacket. The jacket generally surrounds the at least one optical fiber component, the at least one strength member and the at least one ultra-low shrinking filament. The cable can include an interfacial layer interposed between the at least one optical fiber component and the jacket. Additionally, the cable can be riser or plenum rated.
Another aspect of the present invention includes a fiber optic cable having at least one optical fiber component generally stranded around a central member. A first layer including at least one strength member and at least one ultra-low shrinking filament. The first layer being disposed generally between the at least one optical fiber component and a jacket. The at least one ultra-low shrinking filament having a shrinkage of about 0.2% or less when heated and held at about 85xc2x0 C. for about seven days. The jacket generally surrounds the at least one optical fiber component, central member and the first layer. The cable can include an interfacial layer interposed between the at least one optical fiber component and the jacket. Additionally, the cable can be riser or plenum rated.
A further aspect of the present invention includes a fiber optic cable including a first group of tight-buffered optical fiber components being generally adjacent a central member. A first layer being disposed generally between the first group of tight-buffered optical fiber components and a second group of tight-buffered optical fiber components. A second layer being disposed generally between the second group of tight-buffered optical fiber components and a jacket. The jacket generally surrounds the central member, the first and second groups and the first and second layers. One of the layers includes at least one ultra-low shrinking filaments having a shrinkage of about 0.2% or less when heated and held at about 85xc2x0 C. for about seven days. The cable can include an interfacial layer interposed between the central member and the jacket. Additionally, the cable can be riser or plenum rated.
Yet another aspect of the present invention includes a method of manufacturing a fiber optic cable. The method includes paying off at least one optical fiber component, at least one strength member, and at least one ultra-low shrinking filament. The at least one ultra-low shrinking filament having a shrinkage of about 0.2% or less when heated and held at about 85xc2x0 C. for about seven days. Defining a cable core by placing said at least one strength member and at least one ultra-low shrinking filament adjacent to at least one optical fiber component. The method also includes extruding a jacket around said core.